JP4911291B2 - X-ray tomography system - Google Patents

Description

  The present invention relates to an industrial X-ray tomography apparatus.

  In an industrial X-ray tomography apparatus, generally, an X-ray optical axis (a line connecting the X-ray source and the center of the X-ray detector between the X-ray generator and the X-ray detector). ), A structure in which a rotary table that rotates around a rotation axis orthogonal to the structure is used, a subject (inspection object) is mounted on the rotary table, and the rotary table is rotated while irradiating X-rays. X-ray projection data of a subject is collected for each minute rotation angle, and a tomographic image of the subject along a plane orthogonal to the rotation axis is obtained by reconstructing the projection data (see, for example, Patent Document 1).

  In this type of imaging apparatus, the imaging magnification is determined by the distance (SID) between the X-ray focal point of the X-ray generator and the center of the X-ray detector, and the X-ray focal point of the X-ray generator and the subject (rotation center). Although it depends on the ratio of the distance (SOD) to be formed, the combination of these distances is not particularly determined, and largely depends on the experience and intuition of the operator.

Also, there is no particular rule regarding X-ray conditions and imaging conditions such as the tube current and tube voltage of the X-ray generator, and whether or not a metal filter is attached to the light receiving part of the X-ray detector. The reality is that it relies on experience and intuition.
JP 2006-84433 A

  By the way, in the conventional industrial X-ray tomography apparatus as described above, geometric imaging conditions such as SID and SOD, X-ray conditions such as tube current and tube voltage, etc. depend on the intuition and experience of the operator. Therefore, it means that a good tomographic image cannot be obtained quickly for an operator who does not have a certain level of skill.

  The present invention has been made in view of such a situation, and it is an object of the present invention to provide an X-ray tomographic imaging apparatus capable of quickly setting optimum imaging conditions by a simple operation without having skill. .

In order to solve the above problems, an X-ray tomography apparatus according to the present invention connects an X-ray focal point of the X-ray generator and the center of the X-ray detector between the X-ray generator and the X-ray detector. A rotation table that rotates around a rotation axis orthogonal to the X-ray optical axis is provided, and a subject is mounted on the rotation table to rotate while irradiating X-rays. In an X-ray tomography apparatus including reconstruction calculation means for reconstructing a tomographic image of a subject along a plane orthogonal to the rotation axis using the acquired X-ray projection data, a direction along the rotation axis An optical camera that captures the subject from the image, a designation unit that designates a tomographic imaging region on the optical image of the subject by the optical camera, and the rotation table at a position where the tomographic imaging region designated by the designation unit is obtained. Automatically X-ray light A table position control means for moving in a direction, as X-ray condition of the X-ray generator, and several conditions in combination with the presence or absence of the mounting of the metal filter for several tube current and the X-ray detector, the storage means for output of the X-ray detector for each condition is stored and tube voltage such that the predetermined rate of full range, holding the object on the rotary table in a state of being positioned by the table position control means In the state, under several conditions by the combination of the tube current stored in the storage means and the presence or absence of the metal filter, and the X-ray condition applying the tube voltage stored corresponding to each , A search means for rotating the rotary table while irradiating the subject with X-rays to find the rotation angle at which X-rays are most difficult to transmit, and the rotation angle found by the search means Provided with condition setting means for automatically setting an X-ray condition in which the darkest luminance level of the X-ray projection data obtained is zero level or more and the difference between the darkest luminance level and the brightest luminance level is the largest as an optimum condition (Claim 1).

  Here, in the present invention, in the apparatus provided with SID setting means for arbitrarily setting the distance (SID) between the X-ray generation apparatus and the X-ray detection, the table position control means includes the SID. The rotary table is automatically moved so that the tomographic image area designated by the designation means is obtained in the SID set by the setting means, and the storage means detects several types of tube current and X-ray detection. A configuration in which a tube voltage is stored such that the output of the X-ray detector is a predetermined ratio of the full range in each arbitrary SID with respect to several conditions in combination with whether or not a metal filter is attached to the detector ( Claim 2) may be adopted.

  While the present inventors have been engaged in work such as the development of X-ray tomography apparatuses for many years, what kind of a variety of tomographic images including various industrial products are photographed? This is made as a result of grasping the tendency of the photographing conditions that can obtain a corresponding tomographic image even in the subject, and the optimum photographing conditions are set semi-automatically.

The present invention depends on the following viewpoints.
(1) Distance SID formed by the X-ray generator (strictly, the X-ray focal point) and the X-ray detector (strictly, the light receiving unit): There is no particular optimal condition, and the image quality of the tomographic image according to the size Is less affected.
(2) The distance SOD between the X-ray generator and the rotation center of the subject is uniquely determined from the SID and the field of view range (imaging area) to be imaged.
(3) Tube current of the X-ray generator: about 40 μA is frequently used for an object that is relatively difficult to transmit X-rays, and about 80 μA is frequently used for an object that is relatively easy to transmit X-rays. .
(4) X-ray generator tube voltage: Based on the SID and tube current, a value is set at which the output signal level of the X-ray detector is about 80% of the full range.
(5) Metal filter: Used when X-ray transmission is not sufficient. The subject is often made of a material that is very difficult to transmit X-rays.

  Based on the above knowledge, in the present invention, in the X-ray tomography apparatus capable of arbitrarily setting the SID, the SID is arbitrarily set by the operator. Then, the subject on the rotary table is photographed by the optical camera from the direction along the rotation axis, and when the operator designates the photographing region on the optical image, the rotational table is set so that the designated region becomes the tomographic image photographing region. The SOD is determined by automatically moving in the direction of the linear optical axis.

  On the other hand, regarding X-ray conditions, the tube current is limited to several types, for example, two types, and additionally, limited to several types of conditions including whether or not a metal filter is attached to the X-ray detector, and the SID is arbitrarily set. In an apparatus that can perform this, a tube voltage is stored in advance in a storage unit so that the output of the X-ray detector becomes a predetermined ratio of the full range under each of these conditions under an arbitrary SID. Then, for each of the combinations of the tube current and the presence or absence of the metal filter, X-rays are applied to the subject mounted on the rotary table under the tube voltage corresponding to the SID set by the operator. Rotate the subject while irradiating, find the rotation angle at which X-rays are most difficult to transmit, and the darkest luminance level at that position is zero or more, and the difference between the darkest luminance level and the brightest luminance level is the most A large condition is automatically set as the optimum condition.

  Therefore, according to the present invention, the operator only sets an area where a tomographic image is to be obtained on the optical image of the subject, and in addition to the apparatus that can arbitrarily set the SID, the operator only sets the SID appropriately. Therefore, it is not necessary to select any of the tube current, tube voltage, and SOD.

  According to the present invention, it is possible to always determine optimum imaging conditions without depending on the intuition and experience of the operator, and even an unskilled operator can obtain an X-ray tomographic image with good image quality immediately after installation of the apparatus, for example. Obtainable. In addition, since the X-ray conditions are automatically set so that the output level of the X-ray detector becomes a constant ratio of the full range in the set SID, air calibration is performed in advance and stored in a storage medium such as a hard disk. This also has the advantage that air calibration need not be performed each time.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an embodiment of the present invention, and is a diagram illustrating a schematic diagram showing a mechanical configuration and a block diagram showing a system configuration.

  Between the X-ray generator 1 and the X-ray detector 2 arranged so as to face each other, a rotary table 3 for mounting a subject W and applying rotation is arranged. The X-ray optical axis L connecting the X-ray focal point 1a of the X-ray generator 1 and the center of the light receiving unit of the X-ray detector 2 is horizontal, and the rotation axis R of the rotary table 3 is vertical.

  The rotary table 3 is moved by the table moving mechanism 4 in a direction along the X-ray optical axis L (x-axis direction), a direction along the rotary axis R (z-axis direction), and a direction orthogonal to these two directions (y Can be moved in the axial direction). The X-ray detector 2 can be moved in the x-axis direction by the detector moving mechanism 5.

  The X-ray generator 1 generates X-rays corresponding to the tube voltage and tube current supplied from the high voltage generator 6, and the high voltage generator 6 is controlled by the X-ray controller 7. The rotary table 3 and the table moving mechanism 4 are driven and controlled by a drive signal supplied from the table controller 8, and the detector moving mechanism 5 is driven and controlled by a drive signal supplied from the detector position controller 9. The These X-ray controller 7, table controller 8 and detector position controller 9 are placed under the control of the control unit 10.

  The metal filter 2a can be attached to and detached from the light receiving portion of the X-ray detector 2, and the metal filter 2a is attached and detached by driving the filter attaching and detaching mechanism 2b. 10 under control. An operation unit 11 including a mouse, a keyboard, and a joystick is connected to the control unit 10. By operating the operation unit 9, the rotary table 3 is moved in an arbitrary direction, or the X-ray detector 2 is operated. Can be moved in the x-axis direction, and the metal filter 2a can be attached and detached, and the tube voltage and tube current of the X-ray generator 1 can be arbitrarily set.

  Now, a hardware feature in this embodiment is that an optical camera 12 such as a CCD camera is arranged on a rotation axis R above the rotation table 3. A subject W is photographed. The optical camera 12 may be fixed to the rotary table 3 or may be moved in conjunction with the movement of the rotary table 3 in the x-axis, y-axis, or in addition to the z-axis direction. In short, any configuration may be used as long as the subject W on the turntable 3 can always be photographed from the rotation axis R. The output of the optical camera 12 is captured by the control unit 10 via the image data capturing circuit 13 and displayed on the display unit 14 as an optical image viewed from above the subject W. This optical image is used for designation of a tomographic image photographing region by an operator in the following photographing condition setting program.

  Further, the output of the X-ray detector 2 described above is captured as X-ray projection data into the reconstruction calculation unit 16 via the image data capturing circuit 15 when the tomographic image is captured, and the tomographic image of the subject W is constructed. It is used as data for That is, when taking a tomographic image, the subject W is mounted on the rotary table 3 and irradiated with X-rays, and rotated by a minute angle by the rotary table 3, and the X-ray detector 2 is rotated for each minute rotation. X-ray projection data of the subject W as an output is fetched into the reconstruction computation unit 16 via the image capture circuit 15, and a tomographic image of the subject W along the slice plane orthogonal to the rotation axis R is constructed by a known computation, This is displayed on the display 14. On the other hand, in the following imaging condition setting program, the output of the X-ray detector 2 is captured by the image processing unit 17 via the image data capturing circuit 15 and used for setting the X-ray conditions.

  FIG. 2 is a flowchart showing the contents of the photographing condition setting program, and the details thereof will be described below with reference to FIG.

  This program is a so-called semi-automatic condition setting program in which the SOD and X-ray conditions are set by the apparatus side by the operator arbitrarily setting the SID and designating the tomographic imaging region. In this program, among the X-ray conditions, the tube current is limited to two types of 40 μA and 80 μA, and in the case of the tube current of 40 μA, both conditions when the metal filter 2a is mounted and when not mounted. Are set, and a total of three types of conditions are set by these combinations. In the flowchart, the condition for setting the tube current to 40 μA without mounting the metal filter 2a is X-ray condition 1, the condition for setting the tube current to 80 μA without mounting the metal filter 2a is X-ray condition 2, and mounting the metal filter 2a. Thus, the X-ray condition 3 is a condition for setting the tube current to 40 μA.

  For each of these X-ray conditions 1 to 3, the tube voltage at which the output signal level of the X-ray detector 2 is 80% of the full range in each SID is stored in advance. Here, the value of the tube voltage may be determined and stored in advance by checking the output of the X-ray detector 2 for each SID, or the dose is proportional to the square of the tube voltage and the tube current. It may be obtained by calculation based on a characteristic that is proportional to the SID and inversely proportional to the square of the SID.

  In the program, first, the operator mounts the subject W on the turntable 3 and sets an arbitrary SID. In this state, an optical image of the subject W is displayed on the display 14, and a tomographic image capturing area is designated on this image. FIG. 3 shows an example of the display. In this figure, the image of each member by the optical camera 12 is shown with the same reference numerals as those assigned to the respective members in FIG. On the display 11, a tomographic image capturing designation area C is superimposed on the optical image obtained by the optical camera 12 and displayed. The size (diameter) of the imaging designation area C can be changed by operating the operation unit 11. The operator designates a region C where a tomographic image is to be obtained on the optical image of the subject W displayed on the display unit 14 by operating the operation unit 11.

When the tomographic imaging designated area C is determined, the control unit 10 moves and positions the rotary table 3 in the x-axis direction so that the actual tomographic imaging area coincides with the designated area C. The position of the rotary table 3 in the x-axis direction can be calculated by a simple geometric calculation shown in FIG. That is, the SOD can be calculated by the following calculation using the SID at that time, the effective width D of the X-ray detector 2, and the diameter r of the imaging designated region C.
SOD = SID (r / D)

  After completing the setting of the SOD, under the X-ray condition 1, that is, without applying the metal filter 2a with the tube current of 40 μA, the tube voltage at which the output level of the X-ray detector 2 is 80% of the full range. Then, the rotary table 3 is rotated while irradiating X-rays, and X-ray projection data at each rotation angle is taken into the image processing unit 17 to find a rotation angle at which X-rays are hardly transmitted. Then, the difference between the darkest level and the brightest level of the X-ray projection image data obtained at the rotation angle is obtained and stored. This operation is also performed for the X-ray conditions 2 and 3, and among these X-ray conditions 1 to 3, the condition that maximizes the difference is automatically set as the optimum condition.

  The X-ray condition set as described above is a condition in which the output of the X-ray detector 2 is 80% of the full range in the air irradiation state, and the contrast of the X-ray projection data of the subject W is maximized. By photographing, a good tomographic image can be obtained without depending on the intuition and experience of the operator.

  In this embodiment, the above-mentioned X-ray conditions 1 to 3 are set for SIDs that are set under a total of three conditions in which the tube current is fixed to two types and one of them is combined with or without a metal filter. Since the tube current is applied so that the output level of the X-ray detector 2 is 80% of the full range, air calibration is performed in advance and stored in a storage medium such as a hard disk. There is also an advantage that it is not necessary to perform air calibration each time.

  In determining the tube current from the SID under each condition, the output level of the X-ray detector 2 is not limited to 80%, and the tube current value under each condition is 40 μA. Needless to say, the number of conditions is not limited to 80 μA.

  Moreover, in the above embodiment, the example which applied this invention to the X-ray tomography apparatus which can move an X-ray detector to a X-ray optical-axis direction so that SID can be set arbitrarily was shown. However, it goes without saying that the present invention can also be applied to an X-ray tomographic imaging apparatus that does not have such a SID setting function.

In the configuration diagram of the embodiment of the present invention, a schematic diagram showing a mechanical configuration and a block diagram showing a system configuration are shown together. It is a flowchart showing the content of the imaging condition setting program of embodiment of this invention. It is explanatory drawing of the example of a display of the indicator at the time of imaging | photography area specification in embodiment of this invention. It is explanatory drawing of the calculation which calculates | requires SOD from SID and imaging | photography area | region.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray generator 1a X-ray focus 2 X-ray detector 2a Metal filter 2b Filter attaching / detaching mechanism 3 Rotary table 4 Table moving mechanism 5 Detector moving mechanism 6 High voltage generator 7 X-ray controller 8 Table controller 9 Detector position controller DESCRIPTION OF SYMBOLS 10 Control part 11 Operation part 12 Optical camera 13, 15 Image data acquisition circuit 14 Display 16 Reconstruction calculating part 17 Image processing part W Subject

Claims (2)

Between the X-ray generator and the X-ray detector, there is a rotary table that rotates about a rotation axis orthogonal to the X-ray optical axis that connects the X-ray focal point of the X-ray generator and the center of the X-ray detector. Along with a plane perpendicular to the rotation axis, using X-ray projection data taken at every minute angle, with the subject mounted on the rotary table and rotating while irradiating X-rays. In an X-ray tomography apparatus equipped with reconstruction calculation means for reconstructing a tomographic image of a subject,
An optical camera that photographs a subject from a direction along the rotation axis, a designation unit that designates a tomographic imaging region on an optical image of the subject by the optical camera, and a tomographic imaging region designated by the designation unit are obtained. Table position control means for automatically moving the rotary table in the X-ray optical axis direction at a position to be
As X-ray condition of the X-ray generator, and several conditions in combination with the presence or absence of the mounting of the metal filter for several tube current and the X-ray detector, the X-ray detector in each their respective conditions storage means for output to store the tube voltage as a predetermined rate of full range,
While holding the object on the rotary table in a state of being positioned by the table position control means, and several conditions by a combination of the presence or absence of the tube current and the metal filters that have been stored in the storage means, corresponding to each Search means for finding the rotation angle at which the X-ray is most difficult to transmit by rotating the rotary table while irradiating the subject with X-rays under the X-ray conditions to which the stored tube voltage is applied. Optimum condition is an X-ray condition in which the darkest brightness level of the X-ray projection data obtained at the rotation angle found by the search means is zero level or more and the difference between the darkest brightness level and the brightest brightness level is the largest. An X-ray tomography apparatus characterized by comprising condition setting means for automatically setting as   SID setting means for arbitrarily setting a distance (SID) between the X-ray generator and the X-ray detector, and the table position control means uses the designation means in the SID set by the SID setting means. The rotary table is automatically moved so as to obtain a designated tomographic imaging region, and the storage means is a number based on a combination of several types of tube current and whether or not a metal filter is attached to the X-ray detector. 2. The X-ray tomogram according to claim 1, wherein the tube voltage is stored so that the output of the X-ray detector has a predetermined ratio of a full range in each of the arbitrary SIDs for the seed condition. Shooting device.

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